Impact of postfire management on forest regeneration in a managed hemiboreal forest, Estonia

Abstract

Fire is a significant agent for the development of boreal and hemiboreal forests, altering soil and light conditions, affecting seedbanks, and removing seed trees. Burned areas should be managed with care, as inappropriate techniques prolong the regeneration period and reduce the diversity and resilience of stands to disturbances. To study the effects of fire and postfire management on the successional changes in regeneration abundance, species composition and tree height sample plots were established in sandy pine forests in northwestern Estonia on areas burned 2 or 22 years ago. Five types of sample plots were established: (i) areas without fire damage, (ii) burned uncleared areas, (iii) burned forest areas cleared after forest fire, (iv) burned uncleared areas with live trees, and (v) burned uncleared areas with dead trees. Three main tree species common to hemiboreal forests were analyzed: Betula spp., Pinus sylvestris L., and Populus tremula L. Results showed that clearing burned areas after wildfire significantly reduced the abundance of regeneration compared with burned uncleared areas but favored height growth of P. sylvestris in later development. To regenerate and maintain mixed stands after wildfire, retaining some residual trees can facilitate regeneration compared with complete clearing, although a dense stand with live trees or a large amount of deadwood can hinder regeneration.Résumé : Le feu est un agent important de développement des forêts boréales et hémiboréales; il modifie le sol et la luminosité, affecte les banques de graines et élimine les arbres semenciers. Les aires brûlées doivent être aménagées avec soin puisque des techniques inappropriées prolongent la période de régénération et réduisent la diversité et la résilience des peuplements aux perturbations. Pour étudier les effets du feu et de l'aménagement après feu sur les changements successionnels dans l'abondance de régénération, la composition en espèces et la hauteur des arbres, des placettes échantillons ont été établies dans des pinèdes sur sols sablonneux ayant brûlées 2 ou 22 ans auparavant dans le nord-ouest de l'Estonie. Cinq types de placettes échantillons ont été établies : (i) aires exemptes de dommage causé par le feu, (ii) aires brûlées avec des arbres vivants ou morts non récupérés après le feu, (iii) aires brûlées où tous les arbres vivants et morts ont été récoltés après le feu, (iv) aires brûlées avec des arbres vivants non récupérés et (v) aires brûlées avec des arbres morts non récupérés. Trois espèces d'arbre communes aux forêts hémiboréales ont été analysées : Betula spp., Pinus sylvestris L. et Populus tremula L. Les résultats montrent que les aires brûlées et récupérées après le feu étaient associées à une abondance de régénération significativement plus faible que les aires brûlées non récupérées, mais à une plus forte croissance en hauteur de P. sylvestris au cours des stades plus avancés de développement. Pour régénérer et maintenir des peuplements mixtes après un feu, la rétention de quelques arbres résidue...

How Time since Forest Fire Affects Stand Structure, Soil Physical-Chemical Properties and Soil CO2 Efflux in Hemiboreal Scots Pine Forest Fire Chronosequence?

“…The study area (fire chronosequence) is located in hemiboreal vegetation zone, in north-western Estonia, in Vihterpalu and Nõva [2]. The area is flat with no elevation differences and covered with pure Scots pine (Pinus sylvestris L.) stands on sandy soils, regenerated at a different time since forest fires.…”

“…The areas belong to the Calluna and Vaccinium uliginosum site types (Table 1) [16]. The average annual temperature in the area is +5.2 • C. The coldest month is February, with an average temperature of −5.7 • C, and the warmest month is July, with an average temperature of +16.4 • C [2].…”

“…The total area of the forest fire in 2008 (59 • 11 N 23 • 46 E) was about 800 ha and it started at the end of May. The forest stands selected for the current study were 70 years old at the time fire occurred [2]. In August 1997 (59 • 12 N 23 • 49 E) about 700 ha of forest were burned and the forest stands selected for the current study were 45 years old when the fire occurred.…”

“…The time since last fire was first chosen from old inventory data, and later fire occurrence dates were confirmed by taking increment cores at each selected stand. In all areas, three sample plots were established (all together 18 sample plots), that were randomly located in the study areas and the distance between sample plots was at least 100 m. Although the normal practice in Estonia following large-scale disturbances in managed forests is to intervene immediately and clear the stand regardless of whether it will be regenerated naturally or planted [2], we tried to locate our sample plots in areas where the material was not removed after disturbance, thus no management actions (also no planting after disturbance) were carried out. To characterize the stands, circular sample plots with a radius of 11.28 m (400 m 2 ) were established in all areas of fire chronosequence.…”

“…Disturbances are an important factor influencing forest structure formation, composition and forest functioning [1,2]. Forest fires and the long-term recovery from them are important for regional carbon (C) storage because C lost in fires makes a substantial difference to regional C budgets [3].…”